[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete1111 updated this revision to Diff 138187.
Rakete1111 added a comment.

Addressed review comments :)

Thanks!


https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===================================================================
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -137,7 +137,6 @@
     (void)A{n};
     (void)new A(n);
     (void)new A{n};
-    // FIXME: We should diagnose the lack of an initializer here.
     (void)new A;
   }
 }
@@ -150,7 +149,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===================================================================
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A<char>;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10395,12 +10395,22 @@
   // C++11 [dcl.spec.auto]p3
   if (!Init) {
     assert(VDecl && "no init for init capture deduction?");
-    Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
-      << VDecl->getDeclName() << Type;
-    return QualType();
+
+    // Except for class argument deduction, and then for an initializing
+    // declaration only, i.e. no static at class scope or extern.
+    if (!isa<DeducedTemplateSpecializationType>(Deduced) ||
+        VDecl->hasExternalStorage() ||
+        VDecl->isStaticDataMember()) {
+      Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
+        << VDecl->getDeclName() << Type;
+      return QualType();
+    }
   }
 
-  ArrayRef<Expr*> DeduceInits = Init;
+  ArrayRef<Expr*> DeduceInits;
+  if (Init)
+    DeduceInits = Init;
+
   if (DirectInit) {
     if (auto *PL = dyn_cast_or_null<ParenListExpr>(Init))
       DeduceInits = PL->exprs();


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